Longmont
Both. Longmont spans Boulder and Weld counties, and some Longmont-addressed homes aren't in the city at all. Before you shop, know which Longmont a listing is really in. It decides your well, your septic, and your internet.
Boulder
The median single-family home in Boulder sold for $1,275,000 across 2025, and the city adds almost no new houses: a scrape replaces, it doesn't add. So the real decision is which of the three Boulders you can buy, and that comes before any house.